Shield for excavating tunnels and shafts.



W.v M. MoDOWELL.

SHIELD FOB BXGAVATING TUHNBLS AND SHAPTS.

urmuuzon FILED unhu, 191a.

- Patented June 16, 1914.

5 SLIBETSS'HEET 1.

amen Ito's W. M. MoDOWELL. SHIELD FOB EXGAVATING TUNNBLS AND SHAPTS.

APPLICATION rnnnna. 11, ms. Y

' Patented June 16,1914.

5 exams-sum 2.

W. M. MQDOWELL.

SHIELD ron BXOAVATIKNG, TUNNELS AND SHAFTS.

Patented June16, 1914.

5 sums-sum a.

AgPLIOATION FILED APR.11, 1913.

W. M.M0DOWELL. SHIELD FOR EXOAVATING TUNNBLS AND SHAPTS.

APPLICATION FILED APRIL 1918.

Patented June 16,1914

5 SHBBTB-BHEET 4.

I If! I A/f/ I Ill/l I) l!!! g/ I! fl 1 w. M. MCDOWELL, SHIELD FOR EXGAVATING TUNNELS AND SHAPTS.

. APPLIQATIOH FILED APR. 11, 1913. 1,100,142;

Patnted Jime 16, 1914.

6 SHEETS-SHEET 5.

am vmtoz izrlawzawz WILLIE ivr. MQJDOWELL, or Tacoma," wasnrns ron;

SHIELD FOR EXCAVATING'TUNNEIS AND SHAFTS.

me ias.

Specification of Letters Patent.

Application filed April 11, 1913. Serial No. 760,528.

Tocll whom it may concern:

Be it known that I, WILLIE M. MCDOWELL, citizenof the United States, residing at Tacoma, in the county of Pierce and State of Washington, have invented certain new and useful Improvements in. Shields for EX- cavating Tunnels and'Shafts, of which the following is a specification.

My invention relates to the art of tunneling, and particularly to a tunnel shield designed to be disposed at the breast of the tunnel under construction and forced forward as the breast is cut away.

The primary object of my invention is the provision of a tunnel shield so formed that it may be disposed between the false work that supports the tunnel roof and thebreast of the tunnel and forced forward as this breast is cut away.

A further object is to provide a tunnel shield which will protect the workmen cutting away the breast'from any over-break or caving in of the earth or other material from above. a is further object is to so construct the "hield that it will support the great weight of the superincumbent material between the temporary false work and the breast so as not to'allow any settling of the earth.

A further object is to so construct and mount the shield that it may be readily shifted forward from time to time as the work progresses, and in this connection to provide controllable means foruniformly moving theshield forward.

A. still further ob'ect is to provide in connectiorrwith the shield a plurality of hydraulic jacks so mounted as to contact with separated portions of the shield and so controlled as to subject the shield only to auniform strain while it is moving forward.

A further object is to so constructthe shield that it shall afiord protection to the workmen engaged in removing the sections of the skid irons and the roof of the wall plate drift. Y

Another object is to so construct the shield that it shall be supported at its forward end upon the wall plates and at its-rear end upon segments.

Qther objects will appear in the course of the followi description.

drawings wherein;

r t I Figure 1 is a longitudinal verticalsectiohl .best shown in Figs. 4:, 5, 6, 7, 8 and 9.

central vertical plane; Fig. 2 is a transverse vertical section looking from the rear of the tunnel toward the breast thereof andinto the wall plate drifts. Fig. 3 is a vertical section'upon the line 3+3 of Fig. 2 and cutting through the crown of the middle of the tunnel and through one of the wall plate drifts. Fig. 4 is an enlarged vertical sectlio'n of-th'e tunnel shield and the segments supporting the rear of the tunnel shield. Fig. 5

lboking'from the front edge thereof. Fig. 6

is an enlarged fragmentary rear face view of the tunnel shield. Fig. 7 is a perspec- (live view of the elements composing the tunnel shield, the parts being separated. Fig. 8 is a fragmentary cross section on the line 88 of Fig. 5. Fig. 9 is a perspec- {live view of the shield. Fig. 10 is an enlarged'detail section of the cutting edge of the shield. Fig. 11 is a perspective view of one of the shoes supporting the shield.

4 Corresponding and like parts are referred th in the followingdescription and indicated in all the views of the accompanying drawings by the same reference characters.

I will first describe the construction of the shield itself and then describe its method of use; The construction of the shieldr1 is ie shield itself or skin which forms the roof supporting the crown of the tunnel is desighated enerally 2 and is composed preferjably o sections of sheet. metal overlapped and riveted together.

Preferably the shield consists of two 3 sheets of metal as illustrated in Figs. 7 and I0. These plates are designated respectively 4 and5. The longitudinal edges of these plates are abutted against each other and riveted to longitudinal strips 3. The inner plates 4. and 5 are respectively 5 and S5 of an inch in thickness and the which projects beyond the inner plates to form a cutting edge 6 is one inch in thickness, These plates are held together by bolts or rivets 7 the headsof the bolts being countersunk within the plate 6.. As illustrated, the cutting edge projects about four inches in advance of the plates 4 and 5. The shell formed by the plates at and 5 g k v p is about 15 fe'et,'6 inches in length.

My invention is illustr' ted'in-the steam T i the rear end of the shel back as the crown of the shell but are cut of a tunnel under constructiontaken As illustrated in Fi lythe side walls of do not extend as far away as at 8 for a. purpose to helater stated.

Fatented June is, 1914..

is a face elevation of the tunnel shield outer shoe i so t an also began from Fig. 4 that the for- "ward or'cutt' edge of the shell is cut away I 'on each side 10 the lower portion of the arch,

' ajas sit-9 for a purpose which will appear more specificallywhm the. operation of the shell described; f- Supporting tion of the shell of the shield is an arch designated generally 10 and composed of segments' of I-beam 10 more fully illustrated in Figs. and 7. These sections or I-beam so on s" so that when placed together the sections or segments of I-beam will form an approximate arch-shaped member fitting the inside face of the shell as illustrated'clearly .in Figs. 7 and 5. These segments are held in engagement with each other by buttstraps 11 which are riveted to the segments of the I-beam, there being butt-straps on each side of the I-bea-m segments or sections, and they are also heldto ether by buttstraps 12 disposed below llhe junction of each pair of segments. The upper flanges of. the I-beam segments may also be riveted to butt-straps and riveted through the shell, the outer ends of the rivets or bolt holes being countersunk flush with the exterior face of the shell for a purpose heretofore stated. Disposed at the joints between all of those I-beam segments which are located above the cutaway portion 9 of the shield are a plurality of outwardlv projecting trian lar braces designated 13", these braces being held to the inner sheet of theshell by means of angle irons 14 riveted to the braces and to the shell.

I myself to the number of these braces, I preferably provide these triangular braces at the junction between-each two of the sections or segments of I-beam 10 and two more of these braces 13' set equidistantly between the outer braces, all of the braces however being of practically the same construction. The braces are held to the faces of the I- beam segments by means of angle irons 15. The intermediate braces project below the segments and are held to the flanges thereof by angle irons 15".. Projecting rearward from. the arch formed are a plurality of back braces 16 corresponding in construction to the braces 13 but only located between the joints of the I-beam sections. These triangular braces16 are also held to'the rear faces of the I-beam sections by means of angle irons riveted to the braces and to the faces of the I-beam sections and are held to the shell by means of angle irons as described -for the braces 13 as shown clearly in Fig. 8.. Attached to the central segment 10 of the segments, 10, as illustrated in Figs. 5 and 7, is a short section of T-beam or plate flanged at its upper edge and designated 17 which is riveted to the I-beam section 10 and the two braces 13 which are disposed at the the forward por-' cuts are beveled or inclined at their While I do notwish to limit by the I-beam sections,

ends of the I-beam section 10 are extended downward so as to engage with this beam 17. These two braces are designated-13 but they have the same construction as the braces 13 and are'attached to the beams 17 by means of angle irons 15. Attached to opposite points of the arch formed by the I- lower ends of the arch formed bythe segments and supporting said arch, is a shoe which will be hereafter described in detail and which is designated 21. Extending upward from each shoe and attached thereto by butt-straps 25 are pairs of brace rods 26 of channel iron which are riveted at their upper ends to the plate 18 and at their upper ends are also riveted by a butt-strap 27 to apair of'upwardly and centrally inclined braces 28 also formed of channel iron, the upper ends of both pairs of these braces 28 being held together by a butt-strap 29 and r1veted or otherwise attached to the plate 17,

as illustrated, in Fig. 5. Each of the I-bearn segments is formed with an opening 30 or muck-hole whereby earth or other material collecting in front of the supporting arch may be shoveled through to the rear thereof. Projecting inward at the top of the cutaway portion 9 and riveted to the forwardly projecting portions of the crown sheets 2 on each side of the shield are the shelves 31. These as shown in Figs. 4, 5 and 9 project outward. laterally beyond the shell and the inner ends of these shelves are supported by means of downwardly extending hangers 32 riveted to the inner face of the shell as at These shelves or platforms 31 extend forward as far as the cutting ed e of the shield and rearward to the rear wal of each cutaway portion 9.

As before stated, the lower ends of the arch formed by the segments is supported by-means of shoes, these shoes being designated 24. A detail is illustrated in Fig. 11. The shoes are angular in form, that is, formed with a base portion 34 adapted to rest upon the upper face of a wall plate, and with an inwardly disposed, downwardly extending flange 35 adapted to be disposed parallel to the inner faceof the wall plate. The inner end of the shoe is formedwith upwardly extending spaced flan es 36' and 37 connected at their upperends y an inclined web 38 and formed integral with the shoe. The flange 36 is adapted to be attached to a butt-strap 25 view of one of the shoes Mil bears against the inner face of the segment 10 and is riveted thereto. The shoes rest upon wall plates designated 41" and 41. These wall plates are formed of beams notched at their ends for interengagement and connectedby straps 4C2 or in any other suitable manner. The wall plates are 12 inch by 12 inch timbers about 16 feet long, and to these timbers is spiked a 4 inch by 12 inch plank designated 43, also 16 feet long. This plank is spiked longitudinally along the outside edge of the wall plate for the purpose of adding to its strength and at the same time afiord a footing for lagging as will be later described. The wall plate is laid upon a plank foundation designated 44. Planks 45 are placed upon the top of the wall plate to afford a smooth surface upon which skid irons 4.6 are disposed,these skid irons being angular in cross section and resting immediately upon the planks 45. The shoes 24.- rest immediately upon these skid irons. These skid irons prevent the crushing of the wall plate and the planks i5 and permit the shoesto be moved along smoothly in the course of construction. The

wall plates are notched on their upper faces as at 47 for the reception of segment blocks 48 or 48* which are built up in the form of a-series of arches spaced from each other and so disposed as to sup ort that portion .of the shield which exten s rearward from the arch formed by the segments 10. These segment blocks 48 rest one upon the other.

as illustrated in Fig. 2 and are braced apart from each other by spreaders 49. There are two sets of these segment blocks, one set be ing distinguished from the other set by the exponents a, the other set being designated [48". The segment blocks 4E8 are spaced tih from each-other a distance about 4.- feet between centers. The other set 48 while used at the beginning of the forward movement of the. shield, are afterward removed to make more space for concrete lining. Vhen the Spreaders are set feet between centers, the length of the tail sheets or skin plates of the shield is. 11 feetfrom the center of the. I-beam segments to; the ends of the plates. The shield is moved forward by means of a plurality of hydraulic jacks designated 50, base jacks having their forward ends or bases 50" bolted or otherwise attached to the I-beam segments 10. at the junction of each two segments. The pistons of thejacks bear against 10 inch by inehhlocking 5 1 which aredisposed agamst the sage eye.

ment blocks 48. Thus the jacks take their thrust from the timbered section of the completed tunnel. Each of the jacks is equipped with a valve. The bases of the jacks take their thrust at'the joints of the I-beam segment where the heavy butt-straps are audit will be noted that there are braces extending forward from these points and attached to the shell so that the arch is fully braced to stand the pressure of these jacks and so that the pressure of. the jacks shall be distributed-over the whole extent of the shield. It may be noted at this point that in the practical operation of this shield, 50 tons pressure have been applied upon the jacks making a total of 600 tons on the shield,;this pressure being resisted successfully by the particular construction described.

It will be seen from the description that has gone before that the forward end of the shield is slidably supported upon the wall plates while the rear or tail end of the shield, that is to say, the shell, is simply dragged over aportion of the timbered section of the tunnel.

Inasmuch as the jacks are independently operable, it is necessary to provide means for measuring the forward morement of the shield so that all portions of the shield may move together properly. To this end I provide measuring rods 52 graduated in inches, one end of each measuring rod being attached to the shield and there being three measuring rods disposed at different locations, one at each of the steel shoes and one at'the top of the shield. Each measuring rod has notched graduations marked upon it and each measuring rod is attached at its forward end to any suitable point of. the shield by means ofa cotter pin 53 and an The rods are supported in guides 5% attached to the inner faces of the segment blocks 48 so that the rods may slide through these eyes. A ointer 55 is fastened onthe segment blocs so as to coact with the markings on the rods. There is an operator or director of the movement of the shield with two assistants. Thesev assistants are stationed at each of the lateral measuring rods which are attached to the shoes of the a shield and it is their duty to call off the figures to the chief operator a the shield advances. These assistants also under the direction of the chief operator close ofl one or more jacks as the shield advances. The

chief operator of the shield is stationed in convenient location to the upper jacks and notes the position of the top measuring pole. It is by means of closing or opening one or more of thejaeks that the shield is kept under constant control and headed in proper direction with relation to the wall plates.

While the shield as before described may I housed for tunneling where a straight course regulation of the jacks... The shield as illusfrom the tremendous weight which it has which delays the. progress of the tunnel signed to excavate a place for the wall D. 8.- curve. l

'will depend upon the size of the tunnel. In

"consider its operation with particular ref- It will be noted from Figs. 1', and a that the whole areaof the tunneled section is not excavated at one time but that it is The first scctionto be excavated are the wall plate-drifts shown in section in Fig. 3

at all' times maintained, it is possible also to use this shield on a curveby a proper trated forinstance', is capable of being used While have shown an 11 segment arch, such for instance as would be used in building a. very large tunnel, it will be obvious that'the' number of segments to the arch and the diameter of the arch, its height, etc.,

single track tunnels, either 5 or 7 segments are used to form the arch. Of course,'the shield would have the samecurvature as the completed arch. Thus the shield can be built to conform to any sized or any shaped tunnel..

WVhile'I have described what I believe to bethe best and most practical form of my improved shield, and a form which has been thoroughly tested byactual work, I do not wish to be limited to the details of the constructionas set forth as it is obvious that these details maybe varied in manycases to conform, to the special conditions of any particular piece of work without departing from the spirit of the invention. The operationof my invention is as follows:

While .my improved shield is adapted to be used for any kind of, tunneling, I will erence' to soft ground tunneling. The method generally practised in soft ground tunneling is that known-as the poling board -method. In this Well known ting giving away. by breaking or crushing to support, and in-the event of the strutting giving away an over-break is sure to follow constructionby necessitating the" substitu tion of whole timbers for thebroken timbers, and the necessity of excavating the earth fallen from above.

removed in sections and as each section is excavated the-walls thcreofare timbered.

andin elevation in Fig. 2, these drifts being lettered A. ,These wall plate drifts which are two in number and are deplates 41 or 41' are driven with a poling boardlnethod in advance of the general excavation, one on each side. ofxthetunnel, with the floor line about 12 inches below the spring of the roofarch. These wall plate drifts are about 6 feet high and 6 feet wide, affording space for two workmenin each drift. The wall plate drifts are so workedon. Each of these men is protected by the shelf 31 which extends over the rear end of the Wall plate drift. This shelf thus answer two purposes, the other purpose be ing to keep the dirt from running from the roof arch. down into the drift and thus making a very heavy over-break which has to be guarded from at all times. This shelf absolutely prevents .this form of over-break. As the shield is advanced, the 2 by 6 lagging-i which. forms thcroof of each wall plate drift is chopped away a at the point a in Fig. 3 and removed. This is the duty of the man who places the skid irons upon the wall plate. The skid irons are in three sections of 2 feet each and as one is released from under the shoe it is again placed upon the wall plate in advance of the shoe. The heading is that portion of the excavation .for which the shield is primarily intended. The cutting edge of the shield is forced into this heading or'breast.

'It will be noted that the front end of the shield-or shell extends a distance 4 feet 6 inches forward of the I-beam segments and that thus alarge sized working space is afforded for the workmen and the entire face of the breast may be attacked. The roof of the heading section is supported by the front end roof plates of the shields and affords protection to the workmen from loose material falling from above.

In stable material like rock which would ordinarily not crumble down but would have a vertical face, the distance between the for- .ward end of the shield and the turn buckle truss rod 22 is nearly 6 feet, and as the excavation progresses the shield could be advanced without trouble. In soft ground tunneling, however, the workmen excavating the face of the heading stand upon the turn buckle truss rod 22 which affords them a 'good footing and lean against the excavation that the breast of the drift is always about located in those ll-beam sections on a level with the shelves 31, provide means for-5pcnoving the earth that would otherwise pack in front ofthe 18 inch I-beam, this earth preventing the forward progress of the shield. There is a workman stationed at this point to shovelthe earth away from in front of the Lbeam as well as from in front of the space between the inner edge of the f-beam and the outer edge of the channel iron braces,this space also forming a muck hole designated There are four men who take care of dirt in front of the I'-beam segments and under the cutting edge of the roof arch while the shield is advancing and about eight muckers shovel into the conveyer.

In the completed portion ofthe tunnel, that is, that ortion which istemporarily supported by alse work, tracks are laid and I have shown in Fig. 1a jumbo truck and a steam shovel or excavator as operating upon these tracks. The jumbo truck as illustrated in Fig. 2 comprises a platform 0 having depending standards engaging .with trucks, these standards being spaced 'sufliciently apart to permitth'e platform of the b ll excavator to pass beneath the jumbo truck, the excavator being designated D. The excavator D may be of any suitable character but I have illustrated it as a steam shovel,

of an ordinary type. This steam shovel disciarges into a muck' car which moves upon tracks at the side of the first named tracks. I iv Extending fromthe forward end of the jumbo truck is a stage plank designated E and which rests upon the rear end of the breast of the excavation:- -From the forward end-of the stage plank. extends a conveyer F of any suitable type and operated by any suitable means as by the engine G. The forward end of the conveyer is connected to the shield. by means of a chain or other connection If and as. the shield moves forward, the conveyor will follow. The engins G .is also used as a means of forcing motive fluid into the jacks and is connected by means of a pipe line I to theseveral jacks. Men are stationedin front of this conveyor to shovel the earth into it,'-this earth being in turn shoveled downward by the men keeping the heading encavation in trim. "Water may be delivered to the pump driven. by the engine G, a pipe line being laid and keeping pace with theprogress ofv the shield. A hose or'other flexible connection connects the do 1 live eras pipe line andthe suction inletrof the pump. xThe discharge pipe of the-pump is connected to a main header and from this main header connections are made to each of the twelve jacksu Inasmuch as the connection of the pump and jacks is an obvious one and is no part of my invention, .1 hare not described it in detail.

previously stated, the shield is jacked takes the same amount In thev crown bar'system' are made, bolted- Q forward in stages according to the length of the pistons of the jacks. As soon as the shield has. advanced a stage which we will consider to be 4 feet, the jack blocks 51 are taken down and two sets of segment blocks are assembled and put in place. They are then lagged and packed between the top of the arches formed by the segment blocks and beneath the skin plates. There is over 4;

feet, in 'the construction described, between the I-beam segments of the shield and the foremost set of timber segment blocks and. this permits the 4 foot lagging and packing to be readilyput in place. As the shield advances and the earth is cut away beneath this shield, the earth is also cut away at the sides of the excavation and below the wall plates and plumb posts K are put in position as in ordinary tunneling. .This cone pletes the tunneling as far as the false work ii is concerned. Temporary tunnel lining is put in place as the tunnel is extended forward and the tunnel is eventually finished in any desired manner.

With my improved to travel'forward at a rate of one inch a minute including blocking and jacking. In. other words, it takes about one hour and forty minutes to two. and one-half hours to move the shield forward 4 feet. Where the crown bar system is employed, it would take ten pieces of timber 12 inches by 1 2 inches and 32 feet long; 640 pieces of timher 4 inches by 6 inches each 5 feet long, and 88 posts 5 feet long to make 32 of tunnel. With the poling board system it of timber only smaller in size. from to 120 men are usually employed one shift for excavating 4 to 6 feet a day. With the poling board system there are thirty men employeflion a shift for circa-- vating i to- 6 feet ay and with my inr proved shield system thirty men are employed to excavate from 19 1 to 12 feet and no. false timbers have to paused. In other words, the segment blocks-ghee put in place, act to support the tunnel until the permanent work is finished. A a c It will, of course, be obvious that the dimensions and haracter of the shield will to a largeexte'nt depend upon the char actor of the work to bedone and will depend upon the nature of the soil to be penetrated, the size of the tunnel to be excavated,and the dimensions of the temporary timber. lining; In some instances'tem' porary timber lining is for instancei-Ein the use of cast iron lin ng for tunnels but'dnstead cast iron segments together-and assembled inth'e same manner that the timbere'dsegments are assembled. Masonry lining may also be us'edbut with my construction in shield it is possible ,when working rapidly to cause the shield feet not employed, as

10 shafts or like purposes;

thereof and extending cutting edge.--

forward take their thrust from this lining.

The use of this shield of course, not confined to soft ground tunneling as it is possible to use it for tunneling under any circumstances and to use it for sinking What I claim is; i p 1 1." In a tunnel shield, a sup orting arch n'iounted on shoes for forwar movement,

and a shell supported on and movable with the arch, said shell having a cutting edge.

2. In a tunnel shield, a supporting arch, shoes forming the bases for the arch, wall plates on which the shoes are adapted to slide, a shell having its forward end supported on and attached to the arch-and being movable therewith, said shell havin a cutting edge, and braces extending from the face of the arch upward to the forward end of the shell. Y

'3. A tunnel .shield including a supporting, arch formed of beam se ments connected together, a'shell suppor ed on and attached to the arch and having a forward 1 cutting edge, and forwardly and rearwardly 3 fprojecting'braces attached to the beam sections and to theshell.

4."'Atunnel shield including a supporting arch'formed of beam segments con-- nected to each, other, shoes forming the bases of thearch and-supporting the same for sliding; movement, wall. plates on which theshoes'slide, an outer shell supported on and "attached" to the arch, triangular braces attached to the beam'se'gments atthe joints wvardlyjand attached to the shell, theffo'r-.

ward end of theshell being formed with a, cutting edge. 5-. A" tunnel shield comprising an arch formed of "beam segments, and butt-straps,

. forwardly and rearward ly projecting trian- 'gular braces attached 'to and from the-facesiof the beam segments, an

outer shell consisting of aplurality of thickand to the outer shell. I

6. A tunnel shield "including an arch formed of beam segments I-shaped in cross each other, chordal braces rigidly attached to the arch, a tension rod" connected to opposite portions of the arch, and .a shell extending over and supported upon the" areh and having a forward 7. A tunnel shield comprisingan arch formed ofbeam segments, butt-straps conmeeting the beam ijsegzgnents, an outer shell 'supported upon, the-beam segments and attached thereto, shoes formmgtthe bases of,

rwardly and rear of the shield, spacing nesses of material riveted to the beam segl a shield attached at its ments,and'ang1e lIOnS riveted to the braces and horizontally disposed shelves mounted upon the shell at the upper end of the cutaway portion and pro ecting on either side of the shell.

9. A tunnel shield including a supporting-arch, a shell mounted upon. the arch, the'forward end of the shell being cut away from the spring of the arch'.upward, and shelves supported upon the archiat the upper end of the cutaway portion on each s de, of the shell and projecting on either side of the shell.

10. A tunnel shield including a supporting arch, an arch-shaped shell mounted thereon, the forward end-of the shell 9n each side thereof being cut away from the spring of the arch upward to a height approximately equal to that of a .wall plate drift, and horizontal shelves, one on each side of the arch supported at the upper end of the cutaway portions at a height approximately equal to the height of said wall plate drift. 7

v 11. In tunneling apparatus, a supporting arch, a shield mounted on the arch and extending forward and rearward of the,

same, a plurality of segment blocks forming arches and slidably supporting the rear en members disposed between the serles 0 segment blocks, and

- means abutting against said arch andthrustmg against said series of-segment blocks and "spacing members for forcing the arch and the shield carried'thereby' forward. 'pro1ecting 121' In tunneling mechanism, wall plates,

a supporting arch including shoes having slidingengagement upon the wall plates, forward portlon to the arch but projecting forwardly beyond the same, removable supports for the rear end of the shield over which the shield slides, and jacks engaging the arch to force the shield forward.

13. In tunneling mechanism, a supporting arch including shoes for slidingly supporting the, arch upon wall plates, a shell supported at its forward end upon the arch.

pro ecting forwardly beyond the same, means for supporting the rear end of the shell and permitting it to move forward, and jacks having their bases attached to said arch.-

' 14. In tunneling'mechan'ism; oppositelydisposed, parallel wall plates, shoes mounted upon the wall plates for sliding movement therealong, a supporting arch having its ends attached to said shoes, a shell mounted upon the arch near its forward end an projecting forwardly beyond the same, removable segments supporting the rear end of the shield and over which the shield sli'des, jacks having their bases attached to said arch and projecting rearward there from, said jacks taking their thrust against the said segments and acting to move the shield forward.

15. In tunneling mechanism, parallel wall plates, shoes mounted upon the wall plates, each shoe having a horizontal flange and a vertical flange, a supporting arch made up of segments attachedto each other, braces for the arch, a shell attached to the arch near its forward end but projecting forwardly beyond the arch, a plurality of removablesegments slidingly supporting the rear end of the shield, spreaders disposed between the supporting segments, and jacks attached at their bases equidistantly around the arch and taking their thrust against said segments. a v

16. In tunneling mechanism, oppositely disposed, parallel wall plates, shoes 11'lOllI1ted upon the wall platesfor movement therealong, an arch made up of beam segments and butt-straps joining the segments, bydraulic jacks having their bases attached to the arch at the joints betweenthe segments,

a shell mounted upon the'arch and projecting forward and rearward of the same, braces attached to "the arch and to the forward portion ofthe shell,' and means for slidably supporting the rear portion of the shell, said means also adording abutments for the pistons of said hydraulic j acks.

17. A tunneling mechanism including an. arch'made up of beam segments rigidly connected to each other and oppositely disposed shoes attached to the ends of the arch, wall plates upon which said shoes rest and havesliding engagement, a shell mounted upon the arch near its forward end, said shell projecting forward beyond the arch and formed with a cutting edge, the forward end of the shell from a height equal approximately to the height of a wall plate drift being cut inward toward the arch, horizontally disposed shelves forming platforms disposed at the upper end of the cutaway portion, said shelves extending inward of the shell and outward thereof, braces extending from means for the arch, a battery of, jacks having their bases' attached to the inner face of' the arch, and removable means for slidingly supporting the rear ,portion of the shell, said means affording abutments for the jacks.

18. The combination with a tunneling shield 'slidably mounted forforward movement, and means for forcing said tunneling shield forward, of graduated guide rods attached to spaced portions of the shield and movable therewith, and relatively fixed pointers co-acting with the guide rods.

19. A tunnel shield including a shell,a supporting arch therefor attached to the shell, said arch having muck holes formed in its web, and shoes forming the lower ends of the arch and slidingly supporting the same.

20. A tunnel shield including an. arched shell. having aforward cutting edge, an arched support made up of beam segments attached to each other and to the she]1, shoes upon which the lower ends ofthe arch are mounted, and by which the arch is slidingly supported, and horizontally disposed, transversely extending shelves supported from the shield and forward of the arch, the arch being provided with a muck hole behind each shelf.

able supports slidably supporting the rear end of the shield, graduated guide rods attached to separated portions of the shield and movable therewith,- and pointers atthe shield and coaeting with the guide rods. In testimony whereof I affix my signature in presence of two witnesses;

WILLIE ,M. MCDOWELL. a 8.

Witnesses: J B. MITCHELL, THAnnEus HI p.

eopies or this patent may he attained for five cents each, by addressing the Commissioner of Eatents,

Washington, I). 0.

the arch and attached to the shell, bracing 21.- The combination .with a tunneling to move the shield forward; of fixed removtaehed to the supports for the rear endof 

